A variety of soils are common in the institutional and industrial environment. Such soils include organic soils, inorganic soils and soils comprising mixtures thereof. Such soils include food soils, water hardness soils, etc. The soils are common in a variety of locations including in the foods industry. The modern food processing installation produces food products using a variety of continuous and semicontinuous processing units. The units are most efficiently run in a substantially continuous fashion preferably 24 hours a day to achieve substantial productivity and low costs. The safe and effective operation of such process units require periodic maintenance and cleaning operations. Such operation ensures that the equipment operates efficiently and does not introduce into the food product, bacterial contamination or other contamination from food soil residue. Commonly the production units are made from hard surface engineering material including glass, metals including stainless steel, steel, aluminum; and synthetic substances such as acrylic plastics; epoxy, polyimide condensation products, etc. Contamination can occur on an exterior hard surface or in the interior of pipe, pumps, tanks, and other processing units. Known cleaning methods use aqueous cleaning materials that can be applied in a variety of ways to an exterior hard surface or to an interior surface within such units. A vast array of materials have been disclosed as Clean In Place (CIP) cleaner systems. The predominant systems include strongly acidic or basic formulated cleaners and chlorine based materials such as sodium hypochlorite (NaOCl). Sufficient volumes of liquid cleaning materials can be pumped through the piping to ensure that all interior surfaces are contacted with cleaning materials to effectively remove contaminated soils or films.
These cleaning methods known as CIP procedures, clean the surfaces of food processing equipment without any substantial dismantling of the tanks, pumps valves and pipe work of the processing equipment. Because of the elimination of manual cleaning procedures, increased levels of cleanliness can be better assured through better control and reproducibility of the CIP cleaning process. The choice of an effective aqueous cleaning composition is critical to the success of the cleaning procedure because the effectiveness of the procedure depends on the degree of chemical action of the ingredients of the cleaning solution and the mechanical impact of the spray on the residue. A substantial need exists to increase chemical cleaning effectiveness.
With the increasing awareness of ecological concerns and reports about the undesirable impact of many man-made chemicals in the environment, attempts have been made to find more environmentally compatible cleaning compositions. For example, strong acids and alkali tend to change the pH of the environment, active chlorine or hypochlorite can be noxious to many living organisms and is corrosive to many materials used in food processing. Other cleaning materials can have a certain level of undesirability. Further, efforts to reduce the amount of conventional cleaning chemicals used in hard surface cleaning and in the CIP procedures have become important even if the complete elimination of use of such chemicals is not possible. In addition to cleaning hard surfaces, a sanitizing action is important in cleaning food contact surfaces or CIP installation or units. An aqueous sanitizing agent is usually the last agent applied to the equipment in a CIP protocol.
Ozone (O.sub.3) is composed entirely of oxygen atoms. Ozone is a high energy form of oxygen and is unstable at room or higher temperature with the final decomposition product being oxygen. Basic aqueous solutions are known to promote aqueous O.sub.3 decomposition when the gas and aqueous media are mixed. The instability of ozone in aqueous base has resulted in the application of ozone in sanitizer technology at a pH of less than 7. However, the use of alkaline cleaners has significant advantages in cleaning certain types of soils that can be resistant to cleaning at a pH of 7 or less.
Of the different types of soil and residue left on food contacting surfaces, proteinaceous residue, such as residue from dairy products are particularly hard to clean. Kane et al., "Cleaning Chemicals--State of the Knowledge in 1985" discuss chemical cleaners in dairy applications. The most common chemical used in cleaning proteinaceous soil from solid surfaces are alkaline, such as sodium hydroxide. Often a 1 to 3% by weight aqueous sodium hydroxide solution is used. Other chemicals may be added in the cleaning solution to potentiate the cleaning, help solubilize the particles, wet the surfaces, or help prevent precipitation. For example, chlorine (NaOCl) may help in breaking down proteins, sequestrants such as EDTA, NTA, sodium tripolyphosphate, may help in preventing the precipitation of hardness ions, and surfactants may help the wetting of solid surfaces. Ozone has not been used as a cleaning additive in these cleaning applications. An acid rinse and a sanitizer (active chlorine, fatty acid sanitizers, etc.) may be used after the proteinaceous residue has been removed. Other sanitizers include peracetic/hydrogen peroxide (See Bowing et al., U.S. Pat. Nos. 4,051,058 and 4,051,059), perfatty acids (See Wang U.S. Pat. No. 4,040,404, etc.).
While not having been used as a cleaning additive in CIP systems, the use of aqueous ozone solutions are known to be disinfectants or sterilants. Tenney, "Ozone, the Add-nothing Sterilant", Technical Quarterly, vol. 10, No. 1, pp. 35-41 (Master Brewers Association of America 1973) shows the use of ozone to be a useful sterilant in the form of an aqueous ozone solution having no additive ingredients. Bott, "Ozone as a disinfectant in process plant", Food Control, January 1991, pp. 44-49, teaches that ozone can be used as a chlorine replacement for treating industrial water and removing biological growth in the form of microorganisms from hard surfaces. Stillman, "Sanitising treatments for CIP post-rinses", Brewing & Distilling International, March 1990, pp. 24 and 25, teaches that post-rinse CIP treatments need careful control to avoid contaminating sanitized surfaces with microorganisms. Stillman teaches that two basic types of treatments are used, the so-called "add-nothing" physical treatment and biocidal treatments. Add-nothing disinfection procedures include filtration, ultraviolet radiation and heat pasteurization to kill microorganisms prior to rinsing. Chemical treatments can include the use of heavy metal such as silver; the use of chlorine, chlorine dioxide, fatty acids, peroxy fatty acids and others. Nowoczin, German Published Patent Application DE 33 20 841, teaches a three-step dairy CIP cleaning process involving a first step of rinsing milk products from the unit followed by a second cleaning step to remove adherent food residues followed by a third step using a cold water rinse. The improvement suggested by Nowoczin involves injecting aqueous ozone in the second cleaning step. Nowoczin suggests the use of a neutral pH and uses ozone with no chemical additives in the ozone injection. Siegel et al., U.S. Pat. No. 4,898,679, teaches an apparatus and a method for manufacturing an aqueous ozone solution. The method of Siegel et al. involves injecting ozone into water to first kill all the microorganisms in the water, passing the treated water to a second zone where it is saturated with ozone, chilling the saturated ozone and maintaining the ozone solution at high concentrations. Siegel et al. does not disclose the use of chemical additives for the purpose of potentiating the ozone action. Garey et al., "A Comparison of the Effectiveness of Ozone and Chlorine in Controlling Biofouling Within Condensers Using Fresh Water as a Coolant", Ozone: Science and Engineering, Vol. 1, pp. 201-207, 1979, indicate that ozone is a more effective biocide than chlorine and does not produce persistent oxidant residuals similar to known chlorine residuals in waste water. The target of the biocidal activity of the ozone is control of biofouling by environmental microorganisms in fresh water used as a coolant. Grasshoff, "Environmental Aspects of the Use of Alkaline Cleaning Solutions", Federal Dairy Research Centre, pp. 107-114, discusses various aspects of alkaline cleaning solutions that do not contain active oxidants such as peroxide, ozone, or chlorine sanitizers but do contain a variety of cleaners including pyrophosphates, sequestrants, gluconates, surfactants, etc.
The low solubility and instability of ozone in aqueous solution is also well known. Sotelo et al., "Ozone Decomposition in Water: Kinetic Study", Industrial Engineering Chemical Research, 1987, 26, pp. 39-43, shows that ozone decomposition occurs at a variety of pH's but is substantially enhanced as the pH increases past 6. At pH 10, the half life of ozone is about 1 to 10 seconds. In particular, hydroxide radicals, formed from ozone, at pH's greater than 7 rapidly cause ozone to decompose into other oxidative and nonactive species. The role of hydroxyl radical is pointed out in Hoigne et al., "The Role of Hydroxyl Radical Reactions in Ozonation Processes in Aqueous Solutions", Water Research, Vol. 10, pp. 377-386, Pergamon Press 1976. The paper shows that hydroxyl radical formed by hydroxide ion catalytic decomposition of ozone is an active agent in a variety of reactions with organic materials.
Shimamune et al., Japanese Kokai H4-118083 (1992), teaches the treatment of filters with ozone for cleaning purposes. A series of patents discusses aspects of cleaning or sanitizing contact lenses using high energy and ozone compositions including Baron, U.S. Pat. No. 4,063,890; Sibley, U.S. Pat. No. 4,104,187; Hofer et al., U.S. Pat. No. 4,214,014; and Zelez, U.S. Pat. No. 5,098,618. Zelez discloses the use of UV radiation at wavelengths of 185 and 254 nm in the presence of oxygen to reduce the hydrophobicity of the surface of plastic substrates. The radiation produces ozone and atomic oxygen, and the atomic oxygen reacts with the plastic surface to produce the desired hydrophilic effect. Again, there was no mention of the relation of ozone and cleaning adjuvants.
In summary, the prior art indicates that ozone can be used beneficially as a sterilant in the form of a gas and in aqueous solutions at pH's of about 7 or less. However, because of the problems related to the decomposition of ozone in alkaline solutions, the skilled artisan has avoided ozone containing compositions at an alkaline pH or with chemical adjuvants or additives. A substantial need exists for the development of ozone containing cleaning materials in alkaline pH's and for potentiating ozone cleaners in formulated systems. Such pH's are useful for certain types of soil. Further, a substantial need exists for developing compositions using ozone and alkaline ingredients or adjuvants. The combination of these materials can provide cleaning properties not attainable otherwise.